1. Field of the Invention
The present invention relates to a coupling for a vehicle, for use in a power transmission clutch such as a starting clutch of a vehicle.
2. Description of the Related Art
In order to improve road ability, starting and acceleration ability of a vehicle, stability of the vehicle body, and the like, precise control of torque transmission is required of a coupling for a vehicle for use in a power transmission clutch of a vehicle.
A constitution of an electromagnetic coupling 301 as a comparative art is shown in FIG. 3.
A pressing member 319 of a ball cam 317 is coupled to a hub 305 in a spline portion 325. When the ball cam 317 is activated, the pressing member 319 slides along a drive pinion shaft 321. In this case, the pressing member 319 receives frictional resistance generated in the spline portion 325.
A frictional force Fs generated in the spline portion 325 is expressed by the following equations:
In the case of the coupling 301, the spline portion 325 is small in diameter. Specifically, in the equation (2), r is small, and in the equation (1), Fs is large. In other words, the frictional resistance generated in the spline portion 325 is large.
FIG. 4 shows change in transmitted torque (T) to current value (I) exciting an electromagnet 313.
Solid-line curves 203 and 205 indicate respective changes in theoretical transmitted torque (T) of the coupling 301 when the foregoing current value (I) is changed.
Owing to the frictional resistance generated in the spline portion 325, large hysteresis is generated as indicated by the curves 203 and 205.
Accordingly, it becomes difficult to precisely control the torque transmission, and thus it becomes difficult to improve road ability, starting and acceleration ability, stability of the vehicle body, and the like. Moreover, it becomes also difficult to make precise corrections for secular change in the coupling.
As a countermeasure to this, a method is conceived in which the transmitted torque (T) is detected by use of a torque sensor. However, a complicated structure and high cost are unavoidable in this method. Moreover, there remains the fundamental problem of the large hysteresis generated in the control system.
The object of the present invention is to provide a coupling for a vehicle, which is capable of controlling the torque transmission more precisely without using any special means to bring about a cost increase, by reducing the hysteresis when the transmitted torque is increased and decreased.
A first aspect of the present invention is a coupling for a vehicle, comprising: a pilot clutch for generating a pilot torque, the pilot clutch being operated by an operating means; a main clutch for transmitting the transmitted torque, connecting an input torque member and an output torque member, the main clutch being disposed outside the pilot clutch in a radial direction, to which main sliding portions that slide when receiving the transmitted torque are limited; a pressing system comprising any of a unitary member and a plurality of members mutually positioned, the pressing system moving unitarily in a pressing direction; and a coupling mechanism operated by the pilot torque, converting the pilot torque into a pressing force for coupling the main clutch via the pressing system, and amplifying the pressing force.
In such a manner, the main sliding portions are limited to be on the side of the large-diameter main clutch, and thus the distance (radius) r from the shaft center to the gear surface in the foregoing equation (2) becomes large, and the force F generated on the gear surface by receiving the transmitted torque (T) becomes small. Furthermore, if F becomes small, the frictional force Fs generated on the gear surface becomes small in the equation (1).
If the frictional force Fs of the sliding portions receiving the transmitted torque becomes small, then the frictional resistance applied to the pressing system of the main clutch becomes small. Thus, the transmitted torque quickly responds to the increase and the decrease of the current controlling torque transmission.
In the case of disposing the coupling as a power transmission member or of using the coupling in a starting clutch, more precise control of the torque transmission is accomplished, and road ability, starting and acceleration ability, and stability of the vehicle body and the like can be improved to a great extent.
Moreover, correction of the torque transmission in response to secular change of each portion is performed more accurately.
As described above, since the coupling of the present invention can control the torque transmission precisely for a long period of time and stabilize the same, the coupling of the present invention is suitable as apparatus such as the power transmission member and the starting clutch of a vehicle.
Moreover, due to small frictional resistance, a system for detecting transmitted torque by use of a torque sensor is not necessary, thus making it possible to avoid complication of the structure and cost increase, which would accompany the use of such a system.
Moreover, the main clutch is disposed outside the pilot clutch in a radial direction and is made large in diameter, and thus a large torque transmission capacity can be obtained. Accordingly, the main clutch can be constituted to be compact in the axial direction, interference thereof with peripheral members is prevented, and the degree of freedom in layout is increased.
A second aspect of the present invention is the coupling according to the first aspect, wherein the main clutch and the pilot clutch are disposed in a lapped manner in a radial direction. The second aspect can obtain an operation and an effect similar to those in a constitution of the first aspect.
Moreover, the main clutch and the pilot clutch are disposed in the lapped manner in a radial direction, and thus, in the case of using a lubrication mechanism to flushingly supply oil from a shaft center in a radial direction, lubricant oil can be efficiently supplied to the pilot clutch and the main clutch. Therefore, the pilot clutch and the main clutch can be sufficiently lubricated and cooled, and the durability thereof can be greatly improved.
Note that a phrase, xe2x80x9cdisposed in a lapped mannerxe2x80x9d, mentioned herein means that a part or the entirety of a projection of the main clutch in a radial direction is lapped over a projection of the pilot clutch in a radial direction.
A third aspect of the present invention is the coupling according to the first aspect, wherein the main clutch and the pilot clutch comprise outer plates and inner plates, the coupling mechanism comprises a first member and a second member, the pressing system comprises the pilot clutch, the second member of the coupling mechanism, and an outer member, the outer member being connected to the outer plates of the main clutch and the pilot clutch, the outer member being connected to any of the input torque member and the output torque member movably in a pressing direction, and the main sliding portions are limited to being between the outer member and the torque member to which the outer member is connected, between the outer member and the outer plates, or between the inner plates and an inner member, the inner member being connected to the inner plates of the main clutch, the inner member being connected to the first member of the coupling mechanism. The third aspect can obtain an operation and an effect equivalent to those in the constitution of the first aspect.
A fourth aspect of the present invention is the coupling according to the third aspect, wherein the pilot clutch, the second member of the coupling mechanism, and the outer member maintain a positional relation among themselves whilst the pressing system moves. The fourth aspect can obtain an operation and an effect equivalent to those in a constitution of the third aspect.
Moreover, since no change occurs in the relative positional relation among the respective members constituting the pressing system, there are no elements to generate frictional resistance among the members of the pressing system, thus enables the torque transmission to be controlled precisely for a long period of time and to be stabilized.
A fifth aspect of the present invention is the coupling according to the first aspect, wherein the operating means comprises an electromagnet. The fifth aspect can obtain an operation and an effect equivalent to those in the constitution of the first aspect.
In addition, the electromagnet is used as the operating means of the pilot clutch, and thus, for example, unlike in a pressure system, a pump, a driving source and a pipe thereof and the like are not required. Accordingly, since the coupling has a simple structure, the coupling is low in cost, lightweight and compact, with excellent mounting capabilities, and can achieve high reliability owing to no pressure leak.
Moreover, a torque transmission characteristic can be controlled and secular change thereof can be corrected precisely by adjusting the excitation current. And a torque transmission characteristic further stabilized for a long period of time can be obtained.
A sixth aspect of the present invention is the coupling according to the fifth aspect, wherein the electromagnet is fitted in a non-rotational state to a rotor connected to the outer member with a bearing interposed therebetween. The sixth aspect can obtain an operation and an effect equivalent to those in a constitution of the fifth aspect.
In addition to this, since the electromagnet is fitted in a non-rotational state to the rotor coupled to the outer member with a bearing interposed therebetween, the electromagnet moves in an axial direction together with the outer member and the rotor when the clutch is connected and disconnected. However, the electromagnet itself is non-rotational. Accordingly, a special electricity-supplying means for a rotating body such as a slip ring is not necessary, and thus wiring and installation thereof are facilitated.